In order to make room for a mirror to deflect the reflection of the pump, I made a new design with Jammt. Now we use a 50mm lens and a 100mm lens. In this design, the beam size on the 100mm lens is larger, so the position of the waist is further. Since the waist has to stay in the same position as before (the usual position of the crossing point), we put backward the last lens, and this makes room for the mirror. The mirror sends the reflection to a high power beam dump outside the optical board.

Then I measured the pump beam profile. The waist is 36.4um and its position 38.4mm (in the translation stage reference)

 

To align the probe I used a mirror and a prism mirror. the probe has to be at 0.1rad from the incident pump. But the pump is already at 2deg = 0.035rad, so the probe angle has to be  0.1-0.035 = 0.065rad. I made the alignment with the usual pinhole making the beam pass through two positions of the pinhole (start and end):

           x 327.432mm

- center: y 121.255mm     z 34.9mm

- start   : y 121.255+20*0.065mm = 122.555mm   z 14.9mm 

- end    : y 122.555-100*0.065 = 116.055mm     z 114.9mm

 

After making sure that the probe beam is at the right angle, I put a converging lens. First I used the  300mm lens but the beam was too far from the crossing point position and too large. So I used a  250mm lens and measured the beam profile. The waist is 170um and its position 40.4mm (in the translation stage reference). Very close to the pump waist position. But more than 3times larger than the pump.

 

Now there could be a problem because the reflection of the pump passes very close to the probe prism mirror. The beam is quite large and only the tail of the spot touches the prism, but the power will be very high, so, I'm not sure if this will cause some thermal lens effect on the probe.